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This 8 page Class Notes was uploaded by Jess Graff on Wednesday March 9, 2016. The Class Notes belongs to BMS 508 at University of New Hampshire taught by Mary Katherine Lockwood, PhD in Spring 2016. Since its upload, it has received 14 views. For similar materials see Human Anatomy and Physiology II in Biological Sciences at University of New Hampshire.
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Date Created: 03/09/16
BMS 508.03 3/9/16 Chapter 22 (cont) Lymph and Immunity (cont) Special Diseases (cont) • 4 Properties of Immunity 3. Memory • Some active lymphocytes (memory cells): • Stay in circulation • Provide immunity against new exposure 4. Tolerance • Immune system ignores “normal” antigens (self- antigens) • An Introduction to the Immune Response 3. 2 main divisions • Cell-mediated immunity (T cells) • Antibody-mediated immunity (B cells) T Cells and Immunity • 4 Major Types of T Cells Cytotoxic T cells (also called T cClls) • Attack cells infected by viruses • Responsible for cell-mediated immunity Memory T cells • Clone more of themselves in response to “remembered” antigen Helper T cells (also called T ceHls) • Stimulate function of T cells and B cells Suppressor T cells (also called T cellS) • Inhibit function of T cells and B cells • Antigen Presentation T cells only recognize antigens that are bound to glycoproteins in plasma membranes MHC Proteins • The membrane glycoproteins that bind to antigens • Genetically coded in chromosome 6 • The major histocompatibility complex (MHC) • Differs among individuals • Two Classes of MHC Proteins Class I • Found in membranes of all nucleated cells Class II • Found in membranes of antigen-presenting cells (APCs) • Found in lymphocytes • Class I MHC Proteins Pick up small peptides in cell and carry them to the surface • T cells ignore normal peptides • Abnormal peptides or viral proteins activate T cells to destroy cell • Class II MHC Proteins Antigenic fragments • From antigen processing of pathogens • Bind to Class II proteins • Inserted in plasma membrane to stimulate T cells Antigen-presenting cells (APCs) • Responsible for activating T cells against foreign cells and proteins • Phagocytic APCs Free and fixed macrophages • In connective tissues Kupffer cells • Of the liver Microglia • In the CNS • Non-phagocytic APCs Langerhans cells • In the skin Dendritic cells • In lymph nodes and spleen • Antigen Recognition Inactive T cell receptors • Recognize Class I or Class II MHC proteins • Recognize a specific antigen Binding occurs when MHC protein matches antigen • CD Markers Also called cluster of differentiation markers • In T cell membranes • Molecular mechanism of antigen recognition • More than 70 types • Designated by an identifying number • CD3 Receptor Complex Found in all T cells • 2 Important CD Markers CD8 Markers • Found on cytotoxic T cells and suppressor T cells • Respond to antigens on Class I MHC proteins CD4 Markers • Found on helper T cells • Respond to antigens on Class II MHC proteins • CD8 or CD4 Markers Bind to CD3 receptor complex Prepare cell for activation • Costimulation For T cell to be activated, it must be costimulated • By binding to stimulating cell at second site • Which confirms the first signal • Activation of CD8 T Cells Activated by exposure to antigens on MHC proteins • One responds quickly • Producing cytotoxic T cells and memory T cells • The other responds slowly • Producing suppressor T cells • Cytotoxic T (T ) Cells Seek out and immediately destroy target cells • Release perforin • To destroy antigenic plasma membrane • Secrete poisonous lymphotoxin • To destroy target cell • Activate genes in target cell • That cause cell to die • Memory T CelCs Produced with cytotoxic T cells Stay in circulation Immediately form cytotoxic T cells if same antigen appears again • Suppressor T Cells Secrete suppression factors Inhibit responses of T and B cells Act after initial immune response Limit immune reaction to single stimulus • Activation of CD4 T cells Active helper T cells (T ceHls) • Secrete cytokines Memory helper (T ) ceHls • Remain in reserve • Four Functions of Cytokines Stimulate T cell divisions • Produce memory T cellsH • Accelerate cytotoxic T cell maturation Attract and stimulate macrophages Attract and stimulate activity of cytotoxic T cells Promote activation of B cells B Cells and Immunity • B Cells • Responsible for antibody-mediated immunity • Attack antigens by producing specific antibodies • Millions of populations, each with different antibody molecules • B Cell Sensitization • Corresponding antigens in interstitial fluids bind to B cell receptors • B cell prepares for activation • Preparation process is sensitization • During sensitization, antigens are: • Taken into the B cell • Processed • Reappear on surface, bound to Class II MHC protein • Helper T Cells • Sensitized B cell is prepared for activation but needs helper T cell activated by same antigen • B Cell Activation • Helper T cell binds to MHC complex • Secretes cytokines that promote B cell activation and division • B Cell Division • Activated B cell divides into: • Plasma cells • Memory B cells • Plasma Cells • Synthesize and secrete antibodies into interstitial fluid • Memory B Cells • Like memory T cells, remain in reserve to respond to next infection • Antibody Structure • 2 parallel pairs of polypeptide chains • One pair of heavy chains • One pair of light chains • Each chain contains: • Constant segments • Variable segments • Five Heavy-Chain Constant Segments • Determine 5 types of antibodies • IgG • IgE • IgD • IgM • IgA • Variable Segments of Light and Heavy Chains • Determine specificity of antibody molecule • Binding Sites • Free tips of 2 variable segments • Form antigen binding sites of antibody molecule • Which bind to antigenic determinant sites of antigen molecule • Antigen–Antibody Complex • An antibody bound to an antigen • The Antigen–Antibody Complex • A Complete Antigen • Has at least 2 antigenic determinant sites • Binds to both antigen-binding sites of variable segments of antibody • B Cell Sensitization • Exposure to a complete antigen leads to: • B cell sensitization • Immune response • Hapten (Partial Antigens) • Must attach to a carrier molecule to act as a complete antigen • Dangers of Haptens • Antibodies produced will attack both hapten and carrier molecule • If carrier is “normal”: • Antibody attacks normal cells • Example: penicillin allergy
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